The invention relates to a device for dispensing fuel for a gas turbine engine of the type comprising an electrohydraulic converter as the first servo-mechanism (booster) stage, a second servo-mechanism (booster) stage, and a fuel metering slide valve, wherein the thus-dispensed quantity of fuel has a desired relationship to an electric signal transmitted to the electrohydraulic converter.
One task to be accomplished in connection with gas turbine engines is to dispense the quantity of fuel in dependence on certain engine parameters. In most recent times, electrohydraulic devices have been developed for this purpose, making it possible to electrically detect various measuring magnitudes and transform same, etc., and then to feed a signal corresponding to the fuel quantity desired to an electrohydraulic converter. This converter has the purpose of transforming this electrical signal of low power into a hydraulic signal, to amplify this hydraulic signal, and to feed this signal to a fuel metering slide valve. On account of the energy required to actuate this metering slide valve and due to the low power generally generated by the electrohydraulic converter, control devices for larger engines require a further hydraulic booster or servo-mechanism stage. This further booster stage has the purpose of amplifying the signal of the electrohydraulic converter and to activate the fuel metering slide valve.
This metering slide valve is inserted between a fuel feed pump and an injection means so that a change of the stroke of this slide valve corresponds to a change in the fuel feed. In this arrangement, the pressure difference at the metering cross section of the metering slide valve is, in most cases, maintained at a constant value. The metering slide valve uncovers a greater or lesser amount of flow area, so that the amount of fuel flowing to the engine is dependent to the desired extent on the stroke of the metering slide valve.
In gas turbine engines, there is the requirement for large changes in fuel quantity within extremely short periods of time. The booster stage arranged between the electrohydraulic converter and the metering slide valve must be designed so that it provides the required high power. This can result in instabilities.
It is an object of the invention to avoid these instabilities without losing the high regulating speed of the fuel metering slide valve, i.e. the large change in fuel quantity during extremely brief time periods. In this connection, the stabilizing means are desired to be fashioned, insofar as feasible, so that no disadvantages arise with respect to weight and expenses.
In order to solve the aforementioned problems, the invention contemplates providing that the fuel metering slide valve is coupled back to the second booster stage. This feedback is, in particularly preferred embodiments, proportional to the difference of the distances and velocities of the regulating control slide piston of the metering slide valve and of an auxiliary control slide piston of the second booster stage. In certain particularly preferred embodiments, the velocity-proportional feedback force is produced at a displacement piston connected to the auxiliary control slide piston. According to the invention, a feedback action is involved from the metering slide valve, especially by a piston area arranged at the second booster stage, exerting a force on the second booster stage proportional to the difference between the regulating speed of the regulating piston of the metering slide valve and the regulating speed of the just-mentioned auxiliary control slide piston.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, a single embodiment in accordance with the present invention.